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Climb & Conventional Milling "Balanced"

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  • Climb & Conventional Milling "Balanced"

    In an old thread (#29044) there is a statement that reads somewhat as follows:

    "...I balanced the cut so that the conventional and climb components (of the 80mm Face Mill) were"...[equalized]

    Does anyone know how you balance the cut when milling?

    I assume the author was referring to some combination of step-over, overhang, width of cut, entry angle, or position of the 80mm cutter over the workpiece etc. I might even be as simple as 1/4" DOC by 1/4" WOC.

    Background: I have found a lot of information (mostly repetitive) about speeds and feeds when milling with HSS and/or carbide, but little that deals with radial and axial depth of cut or best positioning of the milling tool over the workpiece. Usually the suggestion is "it all depends" without further explanation. Also, the tool makers (Kennametal, Sandvik, Walter et al) focus on using climb milling, while many of us have worn machines (even new machines) that have excess backlash in the table feed, which can cause climb milling techniques to cause exciting things to happen to the tooling and/or workpieces. Very light climb finish cuts are usually not a problem. Adding drag to the gib seems to work most of the time. Wikipedia has a nice explanation with diagrams of conventional vs climb milling for those who want to know about that topic.

    BTW, that Face Mill uses 45° carbide inserts and the author stated that the cutting speed was approx. 540 rpm and that he achieved a beautiful finish.

  • #2 ?
    Location: Helsinki, Finland, Europe


    • #3
      MattiJ Thanks for the reference to the Dapra Paper on Climb Cutter deflection (keep the Climb cut engagement to less than 5% to avoid deflection). The original BBS Forum author was talking about balancing "larger-width cuts by his 80mm (3+) face mill to minimize pull when Climb milling. The CNCcookbook article refers to Dapra discovery of problems when Climb Cutting (which produces a vector, or deflection that is perpendicular to the path of the cutter) when the engagement is more than 5%. But the BBS Forum author was trying to minimize "pull", not push. So, I'm not understanding his comment. BTW, the workpiece ws 5"x7" and made of cast iron. Could it be that cast iron, which can be soft, might have been "pulled" while in Climb mode? Hard to visualize using only 5% of a 3" Face Cutter or describing that as a "larger width" cut.


      • #4
        Basically it is the least "pounding" that you can hear when milling, which is easy when manual milling.
        The concept of "balanced milling" means you are neither pushing the work away, nor pulling it into the cutter
        Consider your cutter like a clock face and it is moving in the 12 o'clock direction . Any material that touches the cutter it at the 3 O'clock position picks up the cutters rotation and is therefore for accelerated to the rear (6 o'clock ) position That is climb milling . This actually occurs with any material presented between 12 and 3 O'clock of the cutters rotation and pulls the work into the cutter ....this is OK if you have ball leadscrews, but deadly for acme threads without backlash control. Now as you move your material to the left side of the 12 o'clock position , the cutter forces the work piece away ( literally pushing it way from the cutter flutes) as it assumes "conventional" mode milling. So depending on the material, the number of flutes and table looseness, you want the material on the left side of 12 O'clock (9-12) to match the material on the right side (12-3) so that pulling or pushing are neutralised and the least force is placed against the leadscrew nut !.
        The exact proportion is a function of the number of flutes (1,2,3,4) . You will find that roughly 2/3rd s of the cut will be to the right of 12 o'clock and 1/3 to the left. So if you have a piece of stock 3/8" wide and you have a cutter 2" in diameter , you will have 1/4" to the right and 1/8" to the left of centerline . But you will see that the pounding will be heavy on the Y axis ! so the cutter is too big. You get the picture . Another factor is the sharpness of the flutes. as they wear and become less sharp you need more stock to the left (9 o'clock) side as cutting forces (climbing ) increase

        Green Bay, WI


        • #5
          I think I get what the guy means...

          You are always doing both when slotting, for instance, so it is balanced. For a face mill, it would be more balanced if the mill is narrower than the part, but is all the way "on" the part, so there is none of it (or very little) hanging out in a non-cutting area. That is like slotting.

          Since conventional cuts push back against the cutter, and climb milling produces some force that will pull the cutter along, doing both should keep you safe from the cutter pulling into the backlash and taking a deeper cut.

          Whatever is hanging out is not compensating, so if most of the conventional cut portion is cutting air, you are losing "compensation", and the cut becomes more like pure climb cutting.

          If you look at the vectors in the climb cutting diagram part, the deeper the cut, the more they rotate toward being backward just like conventional, so that there is no "pulling into the cut", it's stable. The more of the cutter that is working, actually cutting a chip (as with slotting), the more like conventional milling it is as far as the effect on the machine, and the "pulling" turns into "pushing back".
          CNC machines only go through the motions


          • #6
            J Tiers
            When you write "If you look at the vectors in the climb cutting diagram part" are you referring to the Dapra diagram in the referenced CNCcookbook article, above?

            Are you or anyone else reading this aware of more information on this balancing concept? Is there a video somewhere? Another thread here on bbs.hsm? A textbook? Not covered in any of my books.

            Our instructor at Steel Valley VoTech (since closed) was a 50 year lathe guy, and he admitted not using milling machines so much. So I was running a Bridgeport when I exploded a 3/4" HSS endmill into pieces flying just-past two other students. Things were going smoothly just before that happened, then Bam! Fortunately no one got injured, but I was banned from climb milling for the rest of the School Term. On my home Clausing mill, there are occasions when the milling cut is smoother, but mostly there is some hammering when starting into the cut and coming off the cut and any time I don't have two teeth in the cut (4 Tooth).

            Really appreciate your informed replies and I'm starting to understand what I should be doing to make more of the cutting smoother.


            • #7
              yes, that diagram.

              No, that is actually the first place I have seen the vectors diagrammed for various relations of cutter diameter to cut depth.

              Yes, you get slamming when entering the cut. The smaller the mill the worse. I have a small horizontal mill, and it slams quite a bit when starting a cut. A big K&T will just start cutting, it has so much mass that it does not get moved or bothered.
              CNC machines only go through the motions


              • #8
                Originally posted by PointFive View Post

                Are you or anyone else reading this aware of more information on this balancing concept? Is there a video somewhere? Another thread here on bbs.hsm? A textbook? Not covered in any of my books.
                I feel like I have seen the exact same diagram on one of my books but digging trough them would take couple of hours. CNC guys worry about tool deflection but on manual machine you can use the same idea of force vector directions to more safely climb mill.
                End of the cut can be still risky as there is no material in front of the cutter anymore. I just slow down or push the tiny milling machine table forward so that there is no play.
                Location: Helsinki, Finland, Europe


                • #9
                  I'm not a big fan of climb cutting, especially for heavy material removal. However, I find that in some instances I'll get a better surface finish climb cutting with a light DOC.
                  I'm guessing it's because the cutter isn't recirculating chips.



                  • #10
                    They both have their purpose --- I prefer climb milling in most cases as long as I keep the depth of cut in check,

                    and yes it leaves a way better finish than "plow cutting"
                    it also removes more material from the finish cut because your engaging the work piece at maximum interference VS creating a slow ramp up procedure,

                    try it next time your finish cutting something, you can finish cut conventional and then go back over it climb cutting without changing the table and you will see tiny little slivers getting spit out - try the opposite and you won't get that.

                    my endmills seem to last longer with climb cutting - again it confronts the workpiece at maximum interference so the cutter engages and immediately does what it's supposed to do --- cut, once started it finishes the job,

                    conventional is a progressing engagement that creates a vast section of "push off" before the cutter finally decides it has no choice but to dig in, lot's more friction involved with "being on the fence" like that...


                    • #11
                      One of the library books I got out on milling about 20 years ago when I really started taking the whole metal working thing more seriously mentioned conventional milling for heavy removal and climb milling as a finishing cut for the finish. I've always done it that way and liked how each worked out.

                      The issue of heavy cuts with climb milling and blowing up cutters likely has much to do with backlash of the lead screw nuts and play in the gibs. And that's where we run the risk of climb milling into a big cut with a big cutter that pulls itself in and then explodes like Pointfive had happen to him. And that was the reason given in that book on the subject.

                      I've never had a cutter dive in and explode on me but I have noticed that at times the lead screw drag goes to nothing at all when making a climb cut. That's enough of a red flag to let me know that the cutter is trying to self feed and that it's getting VERY close to pulling itself hard into the work. When I've noticed that I've pulled back on the table travel with my other hand to add a little resistive force and finished the cut. But I've always noticed a difference in the handle resistance for conventional vs climb cuts. Maybe wishful thinking but since my climb cuts are generally lighter by far than my conventional cuts it's likely enough to avoid a lunge and grab.

                      On some facing cuts I think we can balance the cut to some extent. But really now big a deal is it if we are not removing big hunks of metal? And besides, we can only have a balanced cut if the cutter is fully engaged or is wider than the work. Cutting a typical rabet will never be at all balanced unless the cutter is just about the same width as the cut being made. Or perhaps that's the point? To pick a cutter size which can be engaged over more of the diameter? If that's the aim then cutting a 1/4" shoulder would be best done in one pass with something like a 5/16 end mill than a 5/8 end mill. But then the 5/16 size isn't as stiff as the 5/8. So clearly we need to take more into consideration than ONLY trying to achieve a balanced cut and we end up going with something like a 3/8" or 1/2" cutter to achieve a reasonable "bury" of the cutter's circumference while using a size which is stronger and more rigid.
                      Chilliwack BC, Canada


                      • #12
                        Sometimes I climb cut just so I don't waste a trip moving the table back to plow cut. Saves wear and tear on the table ways and screws. The way I look at it is you might as well take a cut on the way back.



                        • #13
                          Originally posted by JoeLee View Post
                          Sometimes I climb cut just so I don't waste a trip moving the table back to plow cut. Saves wear and tear on the table ways and screws. The way I look at it is you might as well take a cut on the way back.

                          Just make it a light one or one which is nearly fully engaged.

                          Often when I want a flat surface I'll make multiple back and forth passes with a smaller size end mill just because it's already in the machine. Nothing wrong with bi-directional provided the return "climb" pass also covers a fairly good portion of the climb side as well. Example is a 1/2" end mill removing a 7/16'ish wide pass. That gives us enough on the conventional side to cover off the self feeding pull. And in fact even cutting 3/8" would likely be enough to avoid it pulling itself into the work.

                          What is certainly to be avoided if the DOC is fairly high is to try removing only a 1/16 or so with that same 1/2" cutter. That is going to pull hard and try to dive into the metal.

                          Joe, I'm assuming here that a well engaged cutter is what you meant. And certainly I've done the same thing. Works fine provided we do the return pass with a proper amount of engagement.
                          Last edited by BCRider; 03-31-2018, 11:29 AM.
                          Chilliwack BC, Canada